The present invention relates to apparatus and methods for monitoring a condition such as a chemical concentration of an analyte by monitoring the effect of the condition on a luminescent material.
It has long been recognized that the emission of light by certain luminescent materials is affected by conditions prevailing in the vicinity of the luminescent material. For example, the intensity or lifetime of light emissions from certain luminescent materials are affected by chemical conditions such as the partial pressure of oxygen ("PO.sub.2 ") surrounding the material. Various attempts have been made to use this effect in instruments for monitoring chemical conditions. Ordinarily, such instruments include a luminescent material and appropriate devices for applying excitation light to the luminescent material thereby provoking emission of response light from the luminescent material. The apparatus is arranged to expose the luminescent material to a sample so that the emission may be affected by a chemical condition prevailing within the sample, and to monitor one or more properties of the light emitted by the luminescent material, which properties vary with the condition to be measured. Thus, Khalil et al, U.S. Pat. No. 4,810,655 discloses an instrument for measuring the time dependence of phosphorescence from a phosphorescent material disposed at the end of a fiber optic while the fiber optic is inserted in the sample. The sample may be the blood within a living subject. European Patent Application No. 0,252,578 discloses a similar device for monitoring the time dependence of fluorescence emissions. Although measurement of the decay time characteristics can provide useful information, such measurements generally require rather complex electronics and, hence, do not lend themselves to implementation in a simple and economical instrument.
Parker et al, U.S. Pat. Nos. 4,592,361 and 4,576,173 disclose an apparatus for monitoring the intensity or amplitude of emission from a phosphorescent material in admixture with the tissue of a living subject. These instruments employ various measures to separate the desired long lived phosphorescence emission which is representative of the singlet oxygen content of the tissue from unwanted interfering emissions. Peterson et al, U.S. Pat. No. 4,476,870 discloses an instrument for monitoring oxygen concentration in a living subject by directing excitation light onto a phosphorescent material in contact with the subject and detecting both scattered excitation light and phosphorescence light emitted by the sample. The instrument is arranged to determine the ratio between the scattered excitation light and the phosphorescent light, which ratio serves as a measure of the phosphorescence quenching by oxygen. Such an instrument depends on the stability of the phosphorescent material. Changes in the response characteristics of the phosphorescent material would change the results obtained.
British Published Patent Application No. 2,132,348A discloses a sensor for visual observation. An oxygen-sensitive luminescent material is mounted in a film or layer of an oxygen permeable polymer. A reference luminescent material substantially insensitive to oxygen is mounted adjacent the oxygen-sensitive luminescent material so that the luminescent responses of the two materials can be compared visually, so as to provide a crude measure of oxygen concentration prevailing in the vicinity of the luminescent materials.
European Patent Application No. 0,283,289 discloses an instrument which employs two luminescent materials having different sensitivities to the condition to be sensed. Both luminescent materials are excited into luminescence by excitation light at 350-400 nm wavelength, in the ultraviolet region of the spectrum. The response light from the two luminescent materials is at different wavelengths and is separated by filtering through optical bandpass filters. The ratio of response light amplitudes is determined as a measure of the condition to be monitored.
Despite all of these efforts towards development of luminescence-based instruments for monitoring chemical conditions, there are still significant chemical needs for further improvements.